1. Field of the Invention
This application discloses using ultrasonic testing (UT) as a non-destructive testing (NDT) method for detecting impurities contained in a metal.
2. Description of the Related Art
The prior art generally does not consider non-destructive methods for determining the amount of impurities absorbed by and present in a particular piece of metal. Particularly, UT has never been used to detect impurities in metal because the metal oxide formed on the exterior of the metal interferes with ultrasonic absorption and scattering in the metallic sample. Additionally, for the particular case of hard to detect impurities such as hydrogen, the hydrogen atoms are too small to be detected by conventional UT.
Hydrogen impurities are of particular concern in metal. Hydrogen embrittlement is a common problem in metal: a metal, immersed in water during normal use, absorbs some hydrogen atoms that are present in the water. Absorbing these hydrogen impurities makes the metal brittle, shortening the useful life of the metal. It would be helpful to know whether or not, and to what extent, metal used in an aqueous environment has absorbed hydrogen atoms. More generally, it would be useful to be able to determine the presence and concentration of impurities present in any metal.
3. Summary of the Invention
The present application discloses using UT to determine the concentration of impurities in a metal, notwithstanding the presence of an oxide layer on the surface of the metal under test. This method comprises the steps of: (a) directing a test ultrasonic wave towards the metal under test; (b) measuring as a function of time the amplitudes of the reflected waves reflected from the test metal; (c) detecting a phase deflection in the reflected waves from the reflections caused by an impurity; and (d) relating this phase deflection to the presence and concentration of an impurity in the test metal.